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Accurate projections of future climate scenarios require a detailed understanding of the behavior of Earth’s climate system under varying radiative forcing scenarios. The mid-Piacenzian Warm Period (mPWP; 3.3 – 3.0 Ma) was characterized by atmospheric CO2 concentrations comparable to present-day values (~400 ppmV), while global mean annual temperatures were roughly 2-3 degrees warmer compared to pre-industrial climate (Haywood et al., 2020). Seasonally resolved climate records from fossil bivalve shells offer a snapshot of short-term variability in temperature and salinity under the mild greenhouse conditions of the mPWP (Wichern et al., 2022).In this study, we combine a large dataset of clumped isotope measurements incrementally sampled in fossil shells from the North Sea area during the mPWP with climate model simulations for the same time period using the PlioMIP model comparison framework. This combination of data and models allows us to test whether the climate models in PlioMIP can pick up the sub-annual scale variability in temperature and salinity (reconstructed via the oxygen isotope composition of the paleo-seawater). We show that, in contrast to continental reconstructions used in previous PlioMIP data-model comparisons (Tindall et al., 2022), our shallow marine data is reproduced well by PlioMIP models. On average, both model and data show considerably (4-5°C) warmer summer sea surface temperatures during the mPWP while winter temperatures remain relatively close to pre-industrial values. This suggests that the North Sea region can expect warming concentrated in the summer season in response to elevated atmospheric CO2 conditions.ReferencesHaywood, A. M., Tindall, J. C., Dowsett, H. J., Dolan, A. M., Foley, K. M., Hunter, S. J., Hill, D. J., Chan, W.-L., Abe-Ouchi, A., Stepanek, C., Lohmann, G., Chandan, D., Peltier, W. R., Tan, N., Contoux, C., Ramstein, G., Li, X., Zhang, Z., Guo, C., Nisancioglu, K. H., Zhang, Q., Li, Q., Kamae, Y., Chandler, M. A., Sohl, L. E., Otto-Bliesner, B. L., Feng, R., Brady, E. C., Von der Heydt, A. S., Baatsen, M. L. J., and Lunt, D. J.: A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2, Climate of the Past, 2020.Tindall, J. C., Haywood, A. M., Salzmann, U., Dolan, A. M., and Fletcher, T.: The warm winter paradox in the Pliocene northern high latitudes, Climate of the Past, 18, 1385–1405, https://doi.org/10.5194/cp-18-1385-2022, 2022.Wichern, N. M. A., de Winter, N. J., Johnson, A. L. A., Goolaerts, S., Wesselingh, F., Hamers, M. F., Kaskes, P., Claeys, P., and Ziegler, M.: The fossil bivalve Angulus benedeni benedeni: a potential seasonally resolved stable isotope-based climate archive to investigate Pliocene temperatures in the southern North Sea basin, EGUsphere, 1–53, https://doi.org/10.5194/egusphere-2022-951, 2022.

Growth experiments present a powerful tool for determining the effect of environmental parameters on growth and carbonate composition in biogenic calcifiers. For successful proxy calibration and biomineralization studies, it is vital to exactly identify volumes of carbonate precipitated at precise intervals during the experiment. Here, we investigate the use of strontium labelling in mollusk growth experiments. Three bivalve species (C. edule, M. edulis and O. edulis) were grown under monitored field conditions. The bivalves were regularly exposed to seawater with elevated concentrations of dissolved strontium. In addition, the size of the shells was determined at various stages during the experiment using calliper measurements and digital photography. Trace element profiles were measured in cross sections through the shells of these mollusks using laser ablation ICP-MS and XRF techniques. Our results show that doses of dissolved strontium equivalent to 7-8 times the background marine value are sufficient to produce reproducible peaks in shell incorporated strontium in C. edule and M. edulis shells. No negative effects were observed on shell calcification rates. Lower doses (3-5 times background values) resulted in less clearly identifiable peaks, especially in M. edulis. Strontium spiking labels in shells of O. edulis are more difficult to detect, likely due to their irregular growth. Nevertheless, strontium spiking seems a useful technique for creating time marks in cultured shells and a reproducible way to monitor shell height along the growing season while limiting physical disturbance of the animals. However, accurate reconstructions of growth rates at high time resolution require frequent spiking with high doses of strontium.

Bivalve shells are accretionary biogenic carbonates that yield a record of the organisms’ life history, also with respect to the physiological response to the ambient environmental conditions. This is reflected by variations in the shells’ growth bands, their chemical composition, and morphological features, making them useful tools in paleobiology and paleoenvironmental reconstructions. Corbula gibba is an abundant bivalve species in the Adriatic Sea that is commonly used to resolve questions in age determinations, paleoenvironmental reconstructions and sequence stratigraphic studies [1,2]. Nevertheless, a detailed analysis of its response in growth bands and chemical signatures to environmental variations is currently missing. This study evaluates growth increments and chemical variations in Corbula gibba shells. The shells have been collected alive from the Western Adriatic Sea between Senigallia and Ancona to shed light on the reliability of the Corbula gibba as an archive for (paleo)environmental information. Mutvei's solution has been used [3] to stain the alternating dark and light bundles in the shell, enhancing the visualization of growth increments. High-resolution elemental profiles have been acquired across the outer shells layer using the non-destructive Micro X-ray fluorescence (µ-XRF) technique [4]. The results are compared to available climatic information for Ancona and indicate that Corbula gibba shells record detailed temporal changes in the environment such as tidal fluctuations caused by lunar cycle.[1] Tomašových, A., Gallmetzer, I., Haselmair, A., Kaufman, D., Vidović, J., & Zuschin, M. (2017). Stratigraphic unmixing reveals repeated hypoxia events over the past 500 yr in the northern Adriatic Sea. Geology, 45 (4), 363-366.[2] Tomašových, A., Gallmetzer, I., Haselmair, A., Kaufman, D., Kralj, M., & Cassin, D. et al. (2018). Tracing the effects of eutrophication on molluscan communities in sediment cores: outbreaks of an opportunistic species coincide with reduced bioturbation and high frequency of hypoxia in the Adriatic Sea. Paleobiology, 44 (4), 575-602.[3] Schöne, B., Dunca, E., Fiebig, J., & Pfeiffer, M. (2005). Mutvei's solution: An ideal agent for resolving microgrowth structures of biogenic carbonates. Palaeogeography, Palaeoclimatology, Palaeoecology, 228 (1-2), 149-166.[4] de Winter, N.J., Sinnesael, M., Makarona, C., Vansteenberge, S., Claeys, P., (2017). Trace element analyses of carbonates using portable and micro-X-ray fluorescence: performance and optimization of measurement parameters and strategies. Journal of Analytical Atomic Spectrometry, 32, 1211–1223.

Glendonites are calcite pseudomorphs, that form after the mineral ikaite. Their occurrence in sediments is typically seen as an indication of cold environmental conditions, even when found in predetermined greenhouse climates (Zhou et al., 2015). However, there is still uncertainty about the exact conditions that control glendonite formation and their occurrences are often in conflict with other temperature proxies (Price et al., 2013). Some authors have postulated that the temperature stability range of ikaite could be extended under certain chemical boundary conditions (Teichert and Luppold, 2013). One process that could possibly lead to such circumstances is methane seepage. Here we use clumped isotope thermometry to determine the formation temperature of glendonites. The analysed specimen, comes from a mud volcano, within the upper Paleocene, Basilika Formation near Sveagruva in Svalbard.Thin section analyses and micro-X-ray fluorescence mapping of a glendonite specimen, show that the mineral is highly heterogeneous in terms of trace elemental incorporation. We sampled two distinct phases, for isotope analysis. The clumped isotope composition for both phases are relatively low, indicating apparent formation temperatures >50 degrees, which are unrealistic values for the formation temperature of ikaite. The high Sulfur concentrations, surrounding sediments and low δ13C values of the glendonite are consistent with a formation and decomposition of the ikaite/glendonite caused by the activity of a methane seep. Degassing of CO2 coupled to the methane seepage may have caused isotopic disequilibrium resulting in low clumped isotope values (Bajnai et al., 2020).SourcesBajnai, D., et al., 2020.: ‘Dual clumped isotope thermometry resolves kinetic biases in carbonate formation temperatures’, Nat Commun, 11, 4005, https://doi.org/10.1038/s41467-020-17501-0.Price, G., et al., 2013. Isotopic evidence for long term warmth in the Mesozoic. Sci. Rep. 3 https://doi.org/10.1038/srep01438.Teichert, B. M. A., et al., 2013. ‘Glendonites from an Early Jurassic Methane Seep — Climate or Methane Indicators?’ Palaeogeography, Palaeoclimatology, Palaeoecology, 390, 81–93. https://doi.org/10.1016/j.palaeo.2013.03.001.Zhou, Xiaoli, e.a, 2015. ‘Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity’. The Journal of Geology, 123, 3, 269–81. https://doi.org/10.1086/681918.

Obtaining temperature data from the mid-Piacenzian warm period (mPWP) is a key factor in understanding the coming changes brought upon by anthropogenic climate change. The mPWP, a high-CO2 world with a paleogeography similar to modern times, has been used to validate and improve model retrodictions, which in turn enables assessing the prediction strength of these models1. For the first time, stable isotope analysis has been applied to the extinct tellinid bivalve Angulus benedeni benedeni, originating from the mid-Piacenzian of the Lillo Formation of Belgium in the southern North Sea basin. Multi-annual oxygen isotope records with a seasonal resolution obtained from its shell indicate that this species could live for up to a decade and formed monthly growth increments. From this oxygen isotope record, a clumped-isotope-based mean annual temperature of 12.6 ± 3.6°C was reconstructed. This is 2.1°C warmer than today2,3, 2.6°C warmer than the pre-industrial North Sea2, and in line with global Pliocene temperature estimates of +2-4°C compared to the pre-industrial climate4,5. The pristine nature of the aragonitic shell material was verified through electron backscatter diffraction analysis (EBSD), and backed up by light microscopy, X-ray diffraction, and X-ray fluorescence. The various microstructures as obtained from the EBSD maps have been described, and they provide a template of pristine A. benedeni benedeni material to which potentially altered shells may be compared. The bivalve A. benedeni benedeni is suitable for high resolution isotope-based paleoclimatic reconstruction and it can be used to unravel the marine conditions in the Pliocene North Sea basin at a seasonal scale, yielding enhanced insight into imminent western European climate conditions.1Dowsett, H. J. et al. Assessing confidence in Pliocene sea surface temperatures to evaluate predictive models. Nature Climate Change 2, 365–371 (2012). https://doi.org/10.1038/NCLIMATE1455 2Emeis, K.-C. et al. The North Sea — A shelf sea in the Anthropocene. Journal of Marine Systems 141, 18–33 (2015). https://doi.org/10.1016/j.jmarsys.2014.03.012 3Locarnini, R. A. et al. World Ocean Atlas 2018, Volume 1: Temperature. NOAA Atlas NESDIS 81. A. Mishonov, Technical Editor. 52pp. (2019). https://www.ncei.noaa.gov/access/world-ocean-atlas-2018/ 4Dowsett, H. J. et al. Sea surface temperature of the mid-Piacenzian ocean: a data-model comparison. Scientific reports 3, 1–8 (2013). https://doi.org/10.1038/srep02013 5Haywood, A. M. et al. The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity. Clim. Past 16, 2095–2123 (2020). https://doi.org/10.5194/cp-16-2095-2020

Fast-growing speleothems allow for the reconstruction of palaeoclimate down to a seasonal scale. Additionally, annual lamination in some of these speleothems yields highly accurate age models for these palaeoclimate records, making these speleothems valuable archives for terrestrial climate. In this study, an annually laminated stalagmite from the Han-sur-Lesse cave (Belgium) is used to study the expression of the seasonal cycle in northwestern Europe during the Little Ice Age. More specifically, two historical 12-year-long growth periods (ca. 1593-1605 CE and 1635-1646 CE) and one modern growth period (1960-2010 CE) are analysed on a sub-annual scale for their stable-isotope ratios (δ13C and δ18O) and trace-element (Mg, Sr, Ba, Zn, Y, Pb, U) contents. Seasonal variability in these proxies is confirmed with frequency analysis. Zn, Y and Pb show distinct annual peaks in all three investigated periods related to annual flushing of the soil during winter. A strong seasonal in-phase relationship between Mg, Sr and Ba in the modern growth period reflects a substantial influence of enhanced prior calcite precipitation (PCP). In particular, PCP occurs during summers when recharge of the epikarst is low. This is also evidenced by earlier observations of increased δ13C values during summer. In the 17th century intervals, there is a distinct antiphase relationship between Mg, Sr and Ba, suggesting that processes other than PCP, i.e. varying degrees of incongruent dissolution of dolomite, eventually related to changes in soil activity and/or land-use change are more dominant. The processes controlling seasonal variations in Mg, Sr and Ba in the speleothem appear to change between the 17th century and 1960-2010 CE. The Zn, Y, Pb, and U concentration profiles; stable-isotope ratios; and morphology of the speleothem laminae all point towards increased seasonal amplitude in cave hydrology. Higher seasonal peaks in soil-derived elements (e.g. Zn and Y) and lower concentrations of host-rock-derived elements (e.g. Mg, Sr, Ba) point towards lower residence times in the epikarst and higher flushing rates during the 17th century. These observations reflect an increase in water excess above the cave and recharge of the epikarst, due to a combination of lower summer temperatures and increased winter precipitation during the 17th century. This study indicates that the transfer function controlling Mg, Sr and Ba seasonal variability varies over time. Which process is dominant - either PCP, soil activity or dolomite dissolution - is clearly climate driven and can itself be used as a palaeoenvironment proxy.

Bivalve shells have a long-standing reputation as archives for high-resolution (seasonal scale) (paleo)climate variability due to their incremental growth, yielding accurate shell chronologies, and their abundance, diversity, and high preservation potential in the fossil record (Schöne and Surge, 2012). Capitalizing on innovations in geochemical techniques, high-resolution sclerochronology can now resolve changes in bivalve shell chemistry beyond the daily resolution (e.g. Sano et al., 2012; Warter et al., 2018). When applied on fossil shells, these ultra-high-resolution records have the potential to bridge the gap between climate and weather reconstructions and yield unprecedented information about bivalve paleobiology, extreme weather events in past climates and even astronomical cycles (Warter and Müller, 2017; de Winter et al., 2020; Yan et al., 2020).However, studies of sub-daily scale shell chemistry are almost exclusively limited to giant clams (Tridacna spp.), due to their high growth rates. It is hitherto unknown if and how such diurnal cycles in chemistry differ in other genera across the bivalve clade and/or whether they are exclusive to photosymbiotic clams. In addition, it is not clear whether the daily cycles are formed in response to environmental conditions (e.g. light or temperature sensitivity) or reflect circadian rhythms.To answer these questions, we combine ultra-high-resolution (hourly scale) Laser Ablation ICP-MS trace element profiles through shells of various tridacnid species from the tropical Gulf of Aqaba with profiles through the giant scallop (Pecten maximus) from the temperate Atlantic coast of northwestern France. We observe trace element cycles on in the daily frequency domain in both tridacnids and pectinids. This shows that these diurnal cycles are formed regardless of shell mineralogy (aragonite vs. calcite), living environment (tropical inter-tidal vs. temperate sub-tidal) and occur in highly unrelated bivalve taxa. Our data helps the interpretation of similar records from fossil shells in terms of past (extreme) weather events, climate, and shell growth. Referencesde Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020).Sano, Y. et al. Nature Communications 3, 761 (2012).Schöne, B. R. & Surge, D. M. Treatise Online 24, Volume 1, Chapter 14 (2012).Warter, V., Erez, J. & Müller, W. Palaeogeography, Palaeoclimatology, Palaeoecology 496, 32–47 (2018).Warter, V. & Müller, W. Palaeogeography, Palaeoclimatology, Palaeoecology 465, 362–375 (2017).Yan, H. et al. PNAS 117, 7038–7043 (2020).

Geochemical records from incremental carbonate archives, such as fossil mollusk shells, contain information on climate and environmental change at the resolution of days to decades (e.g. Schöne and Gillikin, 2013; Ivany, 2012). These high-resolution paleoclimate data, providing snapshots of past climate change on a human scale, complement more conventional reconstructions on a geological timescale of thousands to millions of years. Recent innovations in geochemical techniques such as high-resolution trace element and clumped isotope analyses provide the unique potential to improve the accuracy and resolution of these high-resolution climate reconstructions in the near future (see e.g. de Winter et al., 2020a; b; Caldarescu et al., 2021). However, to be able to make the most out of these new techniques requires a more detailed understanding of the timing and mechanisms of mollusk shell growth as well as the relationship between environment and shell chemistry on daily to weekly timescales.The UNBIAS (UNravelling BIvAlve Shell chemistry) project combines investigations on lab-grown modern bivalve shells with reconstructions based on fossil shell material from past greenhouse periods in an attempt to improve our understanding of short-term temperature variability in warm climates. Samples from cultured shells labeled with a novel trace element spiking method are used to calibrate accurate temperature reconstructions from bivalve shells using the state-of-the-art clumped isotope method. As a result, we present a temperature calibration of clumped isotope measurements on aragonitic shell carbonates. New statistical routines are developed to accurately date microsamples within shells relative to the seasonal cycle (ShellChron; de Winter, 2020) and to strategically combine these microsamples for seasonal reconstructions of temperature and salinity from fossil shells (seasonalclumped, de Winter et al., 2020c; de Winter, 2021). We present the first results of this integrated seasonal reconstruction approach on fossil bivalve shells from the Pliocene Warm Period and Late Cretaceous greenhouse of northwestern Europe as well as an outlook on future plans within the UNBIAS project. ReferencesCaldarescu, D. E. et al. Geochimica et Cosmochimica Acta 294, 174–191 (2021).de Winter, N. J. ShellChron v0.2.8: Builds Chronologies from Oxygen Isotope Profiles in Shells. (2020).de Winter, N. J. seasonalclumped v0.3.2: Toolbox for Seasonal Temperature Reconstructions using Clumped Isotope Analyses. (2021).de Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020a).de Winter, N. J. et al. Nature Communications in Earth and Environment (in review; 2020b) doi:10.21203/rs.3.rs-39203/v2.de Winter, N., Agterhuis, T. & Ziegler, M. Climate of the Past Discussions 1–52 (2020c) doi:https://doi.org/10.5194/cp-2020-118.Ivany, L. C. The Paleontological Society Papers 18, 133–166 (2012).Schöne, B. R. & Gillikin, D. P. Palaeogeography, Palaeoclimatology, Palaeoecology 373, 1–5 (2013).

The seasonal variability of sea surface temperatures plays a fundamental role in climate dynamics and species distribution. As such, it is essential to better understand seasonal variability in warm climates of the past. Previous reconstructions of seasonality in deep time are relatively unconstrained, relying on unsupported assumptions such as estimates of seawater composition and negligible seasonal bias. This work presents the first absolute seasonal temperature reconstructions based on clumped isotope measurements in bivalve shells which, critically, do not rely on these assumptions. Our new approach reconstructs highly precise mid-latitude (~50°N) monthly temperatures from individual oyster and rudist shells of the Campanian (78 million years ago) greenhouse period (15—27 °C seasonal range). Our analysis demonstrates that seasonal bias and previous assumptions about sea water oxygen isotope composition can lead to highly inaccurate temperature reconstructions, distorting our understanding of the behavior of greenhouse climates and our ability to model them. Our results agree remarkably well with fully coupled climate model simulations showing greenhouse climates outside the tropics were warmer with higher seasonality than previously thought.

Geochimica et cosmochimica acta 308, 326-352 (2021). doi:10.1016/j.gca.2021.06.012, Published by Elsevier, New York, NY [u.a.]

Giant gastropods are among the largest mollusks in the fossil record, but their potential as paleoseasonality archives has received little attention. Here, we combine stable isotope and trace element analyses with microscopic observations and growth modeling on shells of two species of the gastropod genus Campanile: the extinct Campanile giganteum from Lutetian (~45 Ma) deposits in the Paris Basin (France), the longest gastropod known from the fossil record, and its modern relative Campanile symbolicum from southwestern Australia. The C. giganteum shells contain original aragonite and have pristine nacre in their apertures. We show that these gastropods attained growth rates exceeding 600 mm/year along their helix, depositing over 300 cm3 aragonite per year. High growth rates and excellent preservation make C. giganteum excellent archives for reconstructing environmental change at high (potentially daily) temporal resolution, while providing enough material for methods such as clumped isotope analysis. Growth models show that Campanile gastropods grew nearly year-round, albeit slower in winter. Stable oxygen isotope ratios in modern C. symbolicum faithfully record a seasonal variability of 18–25°C in sea surface temperature, only failing to record the coolest winter temperatures (down to ~16°C). Similarly, C. giganteum specimens likely record a nearly complete seasonal temperature range. Assuming constant sea water isotope composition, their oxygen isotope seasonality of up to 2.5‰ would translate to a Lutetian temperature range of 21–32°C in the Paris Basin. We hypothesize that these high and seasonally variable temperatures formed the breeding ground for the Lutetian shallow marine biodiversity hotspot in the Paris Basin.

The shells of oysters (Family Ostreidae) are predominantly composed of two different calcite microstructures: A dense foliated structure consisting of sheet-like folia (“foliated” microstructure) and a more porous microstructure consisting of less well organized leaf-shaped crystals (“chalky” microstructure). These unique characteristics of oyster shells have been subject to a number of studies, with some authors hypothesizing that the chalky structures are mineralized by bacteria living in the shell (Vermeij, 2014). The formation of these microstructures is of great interest, because the phenomenon is unique in the mollusk phylum and because the shells of oysters are popular archives for paleoclimate and paleoenvironment reconstructions (e.g. Bougeois et al., 2018; de Winter et al., 2018). Previous authors have challenged the bacterially mediated mineralization hypothesis through microstructural observations of different parts of the oyster shell (Checa et al., 2018).Here, we expand on this structural evidence by adding detailed observations of differences in chemical composition between the foliated and chalky microstructures. We combine information on trace element concentrations with stable carbon, oxygen, nitrogen and sulfur isotope ratios as well as carbonate clumped isotope analyses of samples from foliated and chalky structures in multiple modern specimens of Magallana gigas, the Pacific oyster. These analyses shed light on the chemical variability within the oyster shell and how it relates to the occurrence of various calcite microstructures. Given the unique isotopic signature of bacterially mediated calcite, our isotopic analysis results allow us to definitively conclude whether the chalky shell structure in modern oysters was precipitated via symbiotic microbes. Furthermore, the degree of intra-shell chemical variability has implications for paleoclimate and paleoenvirionmental reconstructions from fossil oyster shells, for which the applied trace element and isotope systems function as important proxies. The results of this study therefore yield important recommendations for sampling fossil oyster shells for reconstructions, and provide a baseline for the investigation of chemical variability between shell microstructures throughout the Ostreidae family and the mollusk phylum. ReferencesBougeois, L., Dupont-Nivet, G., De Rafélis, M., Tindall, J. C., Proust, J.-N., Reichart, G.-J., de Nooijer, L. J., Guo, Z. and Ormukov, C.: Asian monsoons and aridification response to Paleogene sea retreat and Neogene westerly shielding indicated by seasonality in Paratethys oysters, Earth and Planetary Science Letters, 485, 99–110, 2018.Checa, A. G., Harper, E. M. and González-Segura, A.: Structure and crystallography of foliated and chalk shell microstructures of the oyster Magallana: the same materials grown under different conditions, Scientific reports, 8(1), 7507, 2018.Vermeij, G. J.: The oyster enigma variations: a hypothesis of microbial calcification, Paleobiology, 40(1), 1–13, 2014.de Winter, N., Vellekoop, J., Vorsselmans, R., Golreihan, A., Soete, J., Petersen, S., Meyer, K., Casadio, S., Speijer, R. and Claeys, P.: An assessment of latest Cretaceous Pycnodonte vesicularis (Lamarck, 1806) shells as records for palaeoseasonality: a multi-proxy investigation, Climate of the Past, 14(6), 725–749, 2018.

In order to assess the potential of the honeycomb oyster Pycnodonte vesicularis for the reconstruction of palaeoseasonality, several specimens recovered from late Maastrichtian strata in the Neuquén Basin (Argentina) were subject to a multi-proxy investigation, involving scanning techniques and trace element and isotopic analysis. Combined CT scanning and light microscopy reveals two calcite microstructures in P. vesicularis shells (vesicular and foliated calcite). Micro-XRF analysis and cathodoluminescence microscopy show that reducing pore fluids were able to migrate through the vesicular portions of the shells (aided by bore holes) and cause recrystallization of the vesicular calcite. This renders the vesicular portions not suitable for palaeoenvironmental reconstruction. In contrast, stable isotope and trace element compositions show that the original chemical composition of the foliated calcite is well-preserved and can be used for the reconstruction of palaeoenvironmental conditions. Stable oxygen and clumped isotope thermometry on carbonate from the dense hinge of the shell yield sea water temperatures of 11°C, while previous TEX86H palaeothermometry yielded much higher temperatures. The difference is ascribed to seasonal bias in the growth of P. vesicularis, causing warm seasons to be underrepresented from the record, while TEX86H palaeothermometry seems to be biased towards warmer surface water temperatures. The multi-proxy approach employed here enables us to differentiate between well-preserved and diagenetically altered portions of the shells and provides an improved methodology for reconstructing palaeoenvironmental conditions in deep time. While establishing a chronology for these shells was complicated by growth cessations and diagenesis, cyclicity in trace elements and stable isotopes allowed for a tentative interpretation of the seasonal cycle in late Maastrichtian palaeoenvironment of the Neuquén Basin. Attempts to independently verify the seasonality in sea water temperature by Mg ∕ Ca ratios of shell calcite are hampered by significant uncertainty due to the lack of proper transfer functions for pycnodontein oysters. Future studies of fossil ostreid bivalves should target dense, foliated calcite rather than sampling bulk or vesicular calcite. Successful application of clumped isotope thermometry on fossil bivalve calcite in this study indicates that temperature seasonality in fossil ostreid bivalves may be constrained by the sequential analysis of well-preserved foliated calcite samples using this method.

Geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub-annual timescales. However, the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment. In this study, records of multiple proxies in three bivalve taxa from the same late Campanian locality in Oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment. Micro-X-Ray Fluorescence mapping allows the localization, discussion and evasion of diagenetically altered parts of the fossil shells. X-Ray Fluorescence line scanning calibrated with Laser Ablation Inductively Coupled Plasma Mass Spectrometry is used to measure trace element profiles through well-preserved calcitic parts of the shells. Records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high-resolution trace element concentration profiles to study sub-annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale. Spectral analysis routines are used to detect cyclicity in stable isotope (δ18O and δ13C) and trace element (Mg/Ca, Sr/Ca, S/Ca and Zn/Ca) records. Differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species-specific physiological effects. Stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 °C around an annual mean of 28 °C, with the shell of the rudistid Torreites sanchezi milovanovici yielding slightly higher average temperatures. The discussion of the application of various Mg/Ca palaeotemperature calibrations on Mg/Ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species. It shows that long-term changes in Mg/Ca ratios in ocean water need to be taken into account and that Mg/Ca ratios in bivalves might be influenced by vital effects. Sr/Ca and S/Ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell, although an influence of local salinity on strontium-to-calcium ratios cannot be excluded. Sub-annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column.

Variations of trace element (e.g. Mg, Sr, Ba, Fe, Zn etc.) concentrations along a speleothem's growth axis constitute important paleoclimate proxies. The use of laboratory micro X-ray fluorescence spectrometry as a fast and cheap alternative for conventional mass spectrometry techniques for trace element analysis on speleothems has been explored in the past and yielded satisfactory results. However, within the speleothem community there is need for an in-depth investigation of the full potential of this analytical technique. Compared to other types of paleoclimate archives, benchtop (μ)XRF analysis on speleothems is analytically more challenging because of the high-crystalline speleothem matrix and the low abundance of the elements of interest. In this study, several speleothem samples with differences in mineralogy (calcite versus aragonite) and composition are investigated. Various instrumental parameters are tested and recommendations are made for future studies applying (μ)XRF analysis to speleothems. Quantification based on a multiple standard calibration and an assessment of the error is carried out. Through validation with mass spectrometry techniques, it is confirmed that benchtop μXRF devises are able to generate speleothem trace element records. Successful results were obtained for Sr, Mg and Fe, while Zn and Ba were quantified in samples characterized by high concentrations. Nevertheless, caution has to be taken when interpreting the results, due to the presence of diffraction caused by the crystallinity of the samples. The elements which provide reliable results are sample specific and depend on the type of matrix and elemental abundance. These findings are applied on an Eemian to early Weichselian stalagmite from the Han-sur-Lesse Cave, Belgium. Time series were constructed for Mg and Sr, creating a multiproxy dataset together with previously obtained stable isotope (δ13C and δ18O) ratios, growth-rate and stalagmite morphology. It appears that Mg and Sr are not primarily controlled by prior calcite precipitation, but rather by changes in vegetation activity above the cave.

WOS:000582677500029; International audience; Horizon scanning is an increasingly common strategy to identify key research needs and frame future agendas in science. Here, we present the results of the first such exercise for the field of sclerochronology, thereby providing an overview of persistent and emergent research questions that should be addressed by future studies. Through online correspondence following the 5th International Sclerochronology Conference in 2019, participants submitted and rated questions that addressed either knowledge gaps or promising applications of sclerochronology. An initial list of 130 questions was compiled based on contributions of conference attendees and reviewed by expert panels formed during the conference. Herein, we present and discuss the 50 questions rated to be of the highest priority, determined through an online survey distributed to sclerochronology community members post the conference. The final list (1) includes important questions related to mechanisms of biological control over biomineralization, (2) highlights state of the art applications of sclerochronological methods and data for solving long-standing questions in other fields such as climate science and ecology, and (3) emphasizes the need for common standards for data management and analysis. Although research priorities are continually reassessed, our list provides a roadmap that can be used to motivate research efforts and advance sclerochronology toward new, and more powerful, applications.

This study presents subdaily resolved chemical records through fossil mollusk shell calcite. Trace element profiles resolve periodic variability across similar to 40-mu m-thin daily growth laminae in a Campanian Torreites sanchezi rudist bivalve. These high-resolution records are combined with seasonally resolved stable isotope and trace element records that allow shell-chemical variability to be discussed on both seasonal and daily scale. A combination of layer counting, spectral analysis of chemical cyclicity and chemical layer counting shows that the rudist precipitated 372 daily laminae per year, demonstrating that length of day has increased since the Late Cretaceous, as predicted by astronomical models. This new approach to determine the length of a solar day in geologic history through multiproxy chemical records at subdaily resolution yields considerably more control on the uncertainty of this estimate. Daily chemical variability exceeds seasonal variability in our records, and cannot be explained by diurnal temperature changes. Instead, we postulate that rudist shell chemistry is driven on a daily scale by changes in light intensity. These results together with those of stable isotope analyses provide strong evidence that Torreites rudists had photosymbionts. Bivalve shell calcite generally preserves well. Therefore, this study paves the way for daily-scale reconstructions of paleoenvironment and sunlight intensity on geologic time scales from bivalve shells, potentially allowing researchers to bridge the gap between climate and weather reconstructions. Such reconstructions improve shell chronologies, document environmental change in warm ecosystems, and widen our understanding of the magnitude of short-term changes during greenhouse climates.

High resolution in situ trace element μXRF maps and profiles were measured on the enamel exposed in cross sections through archaeological human permanent molars from seven Late Neolithic/Early Chalcolithic funerary caves and megalithic graves of north-central Iberia. Changes in concentrations of Fe, Zn and Sr in inward direction into the enamel shed light on diagenetic and endogenous trace element concentrations in archaeological tooth enamel. Most of these profiles resemble sigmoid-shaped leaching profiles, suggesting that a combination of diffusion and advection processes govern the uptake of trace elements into the enamel from pore fluids on the outside of the tooth and in the more porous dentine. The present study shows how diffusion-advection (DA) models can be fitted to these trace element profiles to explain changes in trace element concentrations that happen during diagenesis. DA models explain a major part of the variation observed in leaching profiles into the enamel and can be used to reconstruct endogenous trace element concentrations, leaching times and leaching depth as well as trace element concentrations in ambient pore water during diagenesis. Models of trace element leaching together with trace element mapping reveal that Fe, Zn and Sr concentrations consistently increase during diagenesis, regardless of the type of burial site (i.e. funerary caves vs. megalithic graves). Profiles of Pb concentrations show much smaller concentration gradients, causing DA model fitting to be less accurate. Modelled leaching depths of 300–400 μm warrant a careful approach when sampling for endogenous archaeological tooth enamel for trace element and stable isotope analysis. Results also show that it is possible to reconstruct endogenous trace element concentrations from these samples, even without applying pretreatment procedures, because leaching of trace elements into the enamel often remains limited to the outer 300–400 μm of the enamel on archaeological timescales. Modelled leaching times are about ten times lower than the age of the samples, suggesting that the rate of trace element leaching into tooth enamel slows down or even halts during the burial period.

The impacts of diagenesis on archaeological and palaeontological bone complicate investigations of in-vivo chemical and isotopic characteristics. Such bone is often pre-treated in an attempt to remove diagenetic alteration prior to trace element or isotopic analyses, although very few standardized approaches exist for evaluating pre-treatment effectiveness. In this pilot study, we characterize the diagenetic alteration and assess the impact of acetic acid chemical pre-treatment on the trace element and structural characteristics of four bones from Belgium, including an Early Medieval cremated bone from Broechem and three representative ‘old’ bones of different ages (ca. 40–130 ka) from the Late Pleistocene sedimentary sequence of Scladina Cave. Each bone was analyzed before and after acetic acid pre-treatment using the ‘Perio-spot’ technique and ‘Perios-endos’ profiles. We measured trace element concentrations with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and micro X-ray fluorescence spectroscopy (μXRF). Structural characteristics were investigated with Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). Our results indicate that chemical pre-treatment had little to no significant impact on the trace element content of the Early Medieval cremated bone, had the most impact on the youngest bone from Scladina Cave, and had less impact on the trace element content of two older bones from Scladina Cave. This suggests that the effectiveness of acetic acid chemical pre-treatment is greater for bones undergoing early diagenetic processes, has minimal impact on highly crystalline cremated bone, and may preferentially leach in-vivo signatures from bones undergoing later diagenesis. The weights of leachates removed from each bone also correspond well with their hypothetical diagenetic states, indicating that researchers could potentially assess the diagenetic state of bones by weighing the leachates produced during acetic acid pre-treatment. Therefore, our new approach may provide a valuable step toward effectively and consistently differentiating among in- and ex-vivo trace element signatures, and, by proxy, those of their isotopes, in archaeological and palaeontological bone.

Annually laminated speleothems allow the reconstruction of paleoclimate down to a seasonal scale. In this study, an annually laminated stalagmite from the Han-sur-Lesse Cave (Belgium) is used to study the expression of the seasonal cycle in northwestern Europe during the Little Ice Age. More specifically, two historical 12-year-long growth periods (ca. 1593–1605 CE and 1635–1646 CE) and one modern growth period (1960–2010 CE) are analysed on a sub-annual scale for their stable isotope ratios (δ13C and δ18O) and trace element (Mg, Sr, Ba, Zn, Y, Pb, U) content. Seasonal variability in the proxies is confirmed with frequency analysis. Zn, Y and Pb show distinct annual peaks in all three investigated periods related to annual flushing of the soil during winter. A strong seasonal in phase relationship between Mg, Sr and Ba in the modern growth period reflects a substantial influence of prior calcite precipitation (PCP). In particular, PCP occurs during summers when recharge of the epikarst is low. This is also evidenced by earlier observations of increased δ13C values during summer. In the 17th century intervals, there is a distinct antiphase relationship between Mg, Sr and Ba, suggesting that varying degrees of incongruent dissolution of dolomite control the observed seasonal variations. The processes controlling seasonal variations in Mg, Sr and Ba in the speleothem appear to change between the 17th century and 1960–2010 CE. The Zn, Y, Pb and U concentration profiles, stable isotope ratios and morphology of the speleothem laminae all point towards increased seasonal amplitude in cave hydrology and higher drip water discharge during the 17th century. These observations reflect an increase in water excess above the cave and recharge of the epikarst, due to a combination of lower summer temperatures and increased winter precipitation during the 17th century. This study indicates that the transfer function controlling Mg, Sr and Ba seasonal variability varies over time. Which process is dominant, either PCP or dolomite dissolution, is clearly climate-driven and can thus be used as a paleoclimate proxy itself.

The Marinoan glaciation (a.k.a. the Snowball Earth) represents a profound paleoclimatic anomaly in deep time. However, the detailed mechanism of its termination remains largely unknown. It was hypothesized that massive releases of methane via clathrate destabilization at ~635 Ma may have played a role in terminating the glaciation. A key piece of supporting evidence is the finding of methane-derived authigenic calcite cements (MDACCs, δ13Ccarb values down to –48‰) within the Marinoan cap carbonates in South China. However, a more recent study based on clumped isotope (Δ47) measurements suggests that the MDACCs are hydrothermal (T as high as 476 °C) in origin. If correct, the MDACCs cannot be used to infer paleoenvironments right after the glaciation. To test these contrasting hypotheses (ice vs. fire), we conducted a detailed investigation via μXRF, CL, SEM, and SIMS. The SIMS data show a 60‰ range of δ13Ccarb values with positive values (as high as +6.3‰) exclusively in dolomites and negative values (as low as –53.8‰) in calcites. Both the positive δ13Ccarb values and the lowest δ13Ccarb values are revealed in this study for the first time. Our results show that the dolomite crystals are typically euhedral, anomalously large (up to 200 μm) in size, have positive δ13Ccarb values, and are Mn-poor with dull or red luminescence under CL, with dolomite cores partly or almost completely replaced by low-δ13Ccarb calcite. The calcites have low δ13Ccarb values, are Mn-rich with bright orange luminescence under CL, showing multiple stages of vug-filling cements surrounding the preexisting dolomite crystals. These results suggest that the dolomites have been significantly recrystallized during burial or hydrothermal diagenesis and the MDACCs formed even later, postdating the recrystallized dolomites. We conclude that the MDACCs are post-depositional and formed during late diagenesis. Our conclusion is consistent with the prior work based on clumped isotope analysis. The present study casts further doubt on using MDACCs as evidence for methane clathrate in deep time. The role of methane in terminating the Snowball Earth should be re-assessed.

Fil: de Winter, Niels. Analytical, Environmental and Geo-Chemistry (AMGC), Vrije Universiteit Brussel (VUB). Brussels, Belgium. Fil: Vellekoop, Johan. Analytical, Environmental and Geo-Chemistry (AMGC), Vrije Universiteit Brussel (VUB). Department of Earth and Environmental Science. Belgium. Fil: Vorsselmans, Robin. Department of Earth and Environmental Science. Belgium. Fil: Golreihan, Asefeh. Department of Earth and Environmental Science. Belgium. Fil: Soete, Jeroen. Department of Earth and Environmental Science. Belgium. Fil: Petersen, Sierra. Earth and Environmental Sciences Department, University of Michigan, Ann Arbor. Michigan, USA. Fil: Meyer, Kyle. Earth and Environmental Sciences Department, University of Michigan, Ann Arbor. Michigan, USA. Fil: Casadio, Silvio. Universidad Nacional de Río Negro. Escuela de Geología, Paleontología y Enseñanza de las Ciencias. Río Negro, Argentina. Fil: Speijer, Robert. Department of Earth and Environmental Science, KU Leuven. Heverlee, Belgium. Fil: Claeys, Philippe. Analytical, Environmental and Geo-Chemistry (AMGC), Vrije Universiteit Brussel (VUB). Brussels, Belgium. In order to assess the potential of the honeycomb oyster Pycnodonte vesicularis for the reconstruction of palaeoseasonality, several specimens recovered from late Maastrichtian strata in the Neuquén Basin (Argentina) were subject to a multi-proxy investigation, involving scanning techniques and trace element and isotopic analysis. Combined CT scanning and light microscopy reveals two calcite microstructures in P. vesicularis shells (vesicular and foliated calcite). Micro-XRF analysis and cathodoluminescence microscopy show that reducing pore fluids were able to migrate through the vesicular portions of the shells (aided by bore holes) and cause recrystallization of the vesicular calcite. This renders the vesicular portions not suitable for palaeoenvironmental reconstruction. In contrast, stable isotope and trace element compositions show that the original chemical composition of the foliated calcite is well-preserved and can be used for the reconstruction of palaeoenvironmental conditions. Stable oxygen and clumped isotope thermometry on carbonate from the dense hinge of the shell yield sea water temperatures of 11°C, while previous TEX86H palaeothermometry yielded much higher temperatures. The difference is ascribed to seasonal bias in the growth of P. vesicularis, causing warm seasons to be underrepresented from the record, while TEX86H palaeothermometry seems to be biased towards warmer surface water temperatures. The multi-proxy approach employed here enables us to differentiate between well-preserved and diagenetically altered portions of the shells and provides an improved methodology for reconstructing palaeoenvironmental conditions in deep time. While establishing a chronology for these shells was complicated by growth cessations and diagenesis, cyclicity in trace elements and stable isotopes allowed for a tentative interpretation of the seasonal cycle in late Maastrichtian palaeoenvironment of the Neuquén Basin. Attempts to independently verify the seasonality in sea water temperature by Mg ∕ Ca ratios of shell calcite are hampered by significant uncertainty due to the lack of proper transfer functions for pycnodontein oysters. Future studies of fossil ostreid bivalves should target dense, foliated calcite rather than sampling bulk or vesicular calcite. Successful application of clumped isotope thermometry on fossil bivalve calcite in this study indicates that temperature seasonality in fossil ostreid bivalves may be constrained by the sequential analysis of well-preserved foliated calcite samples using this method. .

The Late Devonian mass extinction was the second of five global mass extinctions that shaped life on Earth during the Phanerozoic Eon, and occurred at the Frasnian– Famennian boundary (FFB, 372 Ma). Here, we focus on this time interval at the famous Steinbruch Schmidt section in Germany. This section includes the well exposed Kellwasser black shale intervals, the FFB, and a U-Pb dated ash layer. In this study, we sampled an interval of 5.3 m around the FFB, with an average sampling interval of 3 cm, leading to a collection of about 200 samples. On every sample, we measured carbon and oxygen stable isotopes, magnetic susceptibility and micro XRF elemental geochemistry. Magnetic susceptibility (MS) and detrital-input-related elements such as Ti and Al are higher during the Kellwasser, and there is a good correlation between Al, K, Ti, Fe and MS. 􀀀13C values are high at and around the Kellwasser levels. We selected the MS, Ti/Al and 􀀀13C signals for spectral analysis, as we expect these proxies to contain the best-preserved astronomical signal. We applied the technique developed by Meyers (2015) on the evaluation of eccentricity-related amplitude modulation independently to the 3 signals. Obtained results for the 3 signals are exactly in the same range, with a sedimentation rate of 0.47 cm/kyr and it allows the transformation of the signal from the distance domain (5.3 m) into the time domain (about a 1100 kyr). If we filter precession from signal and look at its envelope, we can see a clear modulation by 100 kyr cycle, including 5 to 6 precession cycles, as expected for the Devonian. These results are in agreement with the timing proposed by De Vleeschouwer et al. (2017). Furthermore, as in De Vleeschouwer et al. (2007), we have identified a strong obliquity Power at the FFB, which is associated at Steinbruch Schmidt with a low eccentricity power. This would correspond to a period with low seasonality and could have influenced the development of anoxia. This time frame combined with the dating of the ash layer below the FFB boundary (Percival et al., 2018) provides an anchor point for this cyclostratigraphic framework. De Vleeschouwer, D., Da Silva, A.-C., Sinnesael, M., Chen, D., Day, J.E., Whalen, M.T., Guo, Z., Claeys, P., 2017. Timing and pacing of the Late Devonian mass extinction event regulated by eccentricity and obliquity. Nature Communications 8, 2268. Meyers, S.R., 2015. The evaluation of eccentricity-related amplitude modulation and bundling in paleoclimate data: An inverse approach for astrochronologic testing and time scale optimization. Paleoceanography 30, 1625–1640.

The discovery of elevated concentrations of the cosmogenic radionuclide 3He in deep- sea sediments from Ocean Drilling Program (ODP) Site 926 (Atlantic Ocean) and ODP Site 757 (Indian Ocean) points toward ac- cretion of extraterrestrial matter, probably as a result of the catastrophic disruption of a large asteroid that produced the Veritas fam- ily of asteroids at ca. 8.3 ± 0.5 Ma, and which may have had important effects on the global climatic and ecologic systems. Here, we in- vestigated the signatures possibly related to the Veritas event by performing a high- resolution multiproxy stratigraphic analysis through the late Tortonian–early Messinian Monte dei Corvi section near Ancona, Italy. Closely spaced bulk-rock samples through a 36-m-thick section, approximately spanning from ca. 9.9 Ma to ca. 6.4 Ma, show an ~5- fold 3He anomaly starting at ca. 8.5 Ma and returning to background values at ca. 6.9 Ma, con rming the global nature of the event. We then analyzed, at 5 cm intervals, bulk-rock samples for sedimentary and environmen- tal proxies such as magnetic susceptibility, calcium carbonate content, total organic carbon, and bulk carbonate d18O and d13C, through a 21-m-thick section encompassing the 3He anomaly. Available high-resolution sea-surface temperature data (via alkenone analyses) for this site show a temperature decrease starting exactly at the inception of the 3He anomaly. Cyclostratigraphic fast- Fourier-transform spectral analyses of the proxies indicate an age of 8.47 ± 0.05 Ma for the inception of the 3He anomaly. A search for impact ejecta (analogous to what is pres- ent in the late Eocene, where both a 3He anomaly and large-scale impact events are recorded) was not successful. Detailed cy- clostratigraphic analyses of our data suggest that the changes in the stable isotope series and environmental proxy series through this late Tortonian time interval had a common forcing agent, and that perturbations of or- bitally forced climate cycles are present ex- actly through the interval with the enhanced in ux of extraterrestrial 3He. Thus, the che- mostratigraphic evidence for a collisional event that created the Veritas family of aster- oids, coinciding with climate perturbations on Earth, suggests yet another form of inter- action between Earth and the solar system.

Bivalve shells record changes in their environment in the chemical composition of their shells and are frequently used as paleoclimate archives. However, many studies have shown that physiological changes related to growth of the bivalve may overprint these chemical tracers. In the present study, a new approach is presented that models growth and development of bivalve shells without a priori knowledge of the physiology of the species. The model uses digitized growth increments in a cross section of the shell together with basic assumptions of the shape of the shell in order to model changes in shell length, thickness, volume, mass and growth rate at a daily resolution through the lifetime of the bivalve. This approach reconstructs the growth history of bivalves based on their shell without the need for a culture experiment, paving the way for growth rate estimations based on fossil bivalve shells. Combination of the growth model with 2D X-Ray Fluorescence trace element mapping allows the incorporation of trace elements into the shell to be modelled in 3D through the bivalve's lifetime. This approach yields records of integrated total-shell trace element concentrations and accumulation rates, which shed light on the rates and mechanisms by which these trace elements are incorporated into the shells of bivalves. Application of growth and trace element modelling on a set of modern pacific oyster shells of well-known origin and comparison of model results with conventional trace element transects highlights the importance of considering heterogeneity in mineralogy, mineralization rates and chemical composition within the shells of bivalves. These insights lead to a better understanding of the complexity of trace element concentrations in bivalve shells, which can then be applied as proxies for the reconstruction of sub-annual changes in palaeoenvironmental conditions over geological timescales.

The study of stable isotopes in fossil bioapatite has yielded useful results and has shown that bioapatites are able to faithfully record paleo-environmental and paleo-climatic parameters from archeological to geological timescales. In an effort to establish new proxies for the study of bioapatites, intra-tooth records of enamel carbonate stable isotope ratios from a modern horse are compared with trace element profiles measured using laboratory micro X-Ray Fluorescence scanning. Using known patterns of tooth eruption and the relationship between stable oxygen isotopes and local temperature seasonality, an age model is constructed that links records from six cheek upper right teeth from the second premolar to the third molar. When plotted on this age model, the trace element ratios from horse tooth enamel show a seasonal pattern with a small shift in phase compared to stable oxygen isotope ratios. While stable oxygen and carbon isotopes in tooth enamel are forced respectively by the state of the hydrological cycle and the animal's diet, we argue that the seasonal signal in trace elements reflects seasonal changes in dust intake and diet of the animal. The latter explanation is in agreement with seasonal changes observed in carbon isotopes of the same teeth. This external forcing of trace element composition in mammal tooth enamel implies that trace element ratios may be used as proxies for seasonal changes in paleo-environment and paleo-diet.

Bioapatite from mammal tooth enamel is a popular biomineral used in the reconstruction of palaeoenvironment and palaeodiet. It records information about the animal’s environment and diet on a sub-annual scale and is proven to be highly resistant to diagenesis, allowing the preservation of its original chemical composition through archaeological and geological timescales. In this study, stable carbon and oxygen isotope analysis are used as a stepping stone to investigate the use of other chemical proxies for the reconstruction of environment and diet from mammal teeth. Concentration profiles of trace element distributions (measured with µXRF and cross-validated with Laser Ablation ICP-MS) and stable isotope ratios ( 13Cap, 18Oc & 18Op) are combined to test the reliability of trace element profiles from mammal teeth in recording seasonal changes in environment and diet of the animal. A method is presented that links the various geochemical records within a tooth sequence using mineralization sequences and oxygen isotope seasonality. This way, a 3 year trace element and stable isotope record from horse tooth enamel is created showing seasonal variation in trace elements and isotope ratios linked to changes in climatic conditions and diet through the animal’s lifetime. This study shows how an entire new set of trace element proxies, that can be measured quickly and non-destructively, may yield information on palaeoenvironment and palaeodiet. These trace element measurements yield information from precious archaeological samples that could otherwise be obtained solely through destructive sampling. The versatility of the µXRF and LA- ICP-MS methods opens up a wide range of applications for trace element analysis in archaeology.

In the study of archaeological and fossil bone assemblages, diagenesis is an important factor to consider as it will affect the elemental and isotope composition of bone and teeth. Indeed, the carbonates present in bone and tooth apatite are prone to exchange with the surrounding environment. Thankfully, oxygen in also present in the phosphate fraction of bioapatites which is much less prone to exchanges than carbonates. Furthermore, these are present in much larger quantities allowing the analyses of small samples, which is crucial when dealing with precious archaeological and fossil specimens. Comparing the oxygen isotope ratios of the carbonates and phosphates provides insights into the degradation processes bioapatites underwent through time and allows for a better understanding of the exchanges that occurred between bioapatites and the burial environment. This paper presents preliminary results of δ18Op and δ18Oc analyses of a wide range of bioapatites from different contexts, highlights methodological difficulties, and discusses the interpretation of these results in the frame of diagenesis and palaeoenvironmental reconstructions.

Micro-X-ray fluorescence (μXRF) spectrometry is a non-destructive method, which allows rapid identification and mapping of elemental distributions in a wide variety of samples. The recent acquisition of a Bruker Tornado M4 μXRF spectrometer allowed characterization of element distributions in dinosaur bone and eggshell specimens from different localities. Most notably, we used μXRF to investigate the oldest known terrestrial vertebrate eggshells, belonging to Early Jurassic sauropodomorph dinosaurs from South Africa, Argentina and China. With μXRF scans, we were able to identify small fragments of thin eggshell, which would otherwise be difficult to document with classical microscopy or scanning electron microscopy methods. The calcium of the calcareous eggshell and phosphorus of remnants of the membrane are clearly distinguishable from the surrounding matrix. Raman spectroscopic analysis confirmed the respective calcitic and phosphatic nature of the calcareous and membranous layers. In fossil dinosaur bone, calcium and phosphorus are generally dominant elements in the bone tissues, but vascular spaces and other cavities function as a sponge for diagenetic elements such as iron, strontium, yttrium but also uranium and other Rare Earth Elements (REE). Consequently, REE and other trace elements can be a powerful tool for taphonomic investigations. Moreover, the unique patterns of REE, and other trace element concentrations of fossils and fossil sites, also open the potential for application of μXRF to provide a chemical fingerprint of fossil localities. Such fingerprints may ultimately be used to target illegal fossil trade and potentially help resolve legal issues surrounding fossils with questionable provenance. Nonetheless, proper comparative standards need to be established using classical acid solution and/or other mass spectrometry methods, before an extensive database of fossil locality trace element fingerprints can be compiled.

Deep marine successions of early Campanian age from DSDP site 516F drilled at low paleolatitudes in the South Atlantic reveal distinct sub-Milankovitch variability in addition to precession, obliquity and eccentricity related variations. Elemental abundance ratios point to a similar climatic origin for these variations and exclude a quadripartite structure as an explanation for the inferred semi-precession cyclicity in the magnetic susceptibility (MS) signal as observed in the Mediterranean Neogene for precession related cycles. However, semi-precession cycles as suggested by previous work are likely an artifact reflecting the first harmonic of the precession signal. The sub-Milankovitch variability, especially in MS, is best approximated by a ~ 7 kyr cycle as shown by spectral analysis and bandpass filtering. The presence of sub-Milankovitch cycles with a period similar to that of Heinrich events of the last glacial cycle is consistent with linking the latter to low-latitude climate change caused by a non-linear response to precession induced variations in insolation between the tropics.

Supplementary data belonging to the manuscript entitled: "Absolute seasonal temperature estimates for a greenhouse climate state" by de Winter et al.